Supercontinuum generation...

Optical supercontinuum

An optical supercontinuum is broadband coherent light generated when a short laser pulse causes a nonlinear effect in a material. It is unique in possessing both the spectral width of a conventional white light source and the coherence properties of a laser. A striking nonlinear process, it has many applications, the foremost being a new time standard which merited part of the 2005 Nobel Prize.

Supercontinuum research at CUDOS

Our aim is to understand and control the individual processes behind supercontinuum generation. We achieve this by modifying the waveguide properties longitudinally so that the pulse 'feels' different conditions as it evolves and spectrally broadens.

Fig. 3 – Femtosecond source for supercontinuum experiments

Highly nonlinear chalcognide fibre, drawn into a taper to increase power concentration in the glass allows for low power supercontinuum generation. The expertise at CUDOS in both chalcogenide glasses and fibre tapers provides a fertile ground for experiments in ultra-low threshold supercontinuum generation.

Numerical studies of supercontinuum

We use numerical codes to assist in the design of longitudinally varying fibres for supercontinuum generation.

Fig. 4  Simulation of supercontinuum generation in a chalcogenide taper. The top section shows the effect of two photon absorption on supercontinuum generation.

Nonlinear pulse propagation in ARROW fibers

We investigate femtosecond pulse propagation in a microstructured optical fiber consisting of a silica core surrounded by air holes which are filled with a high index fluid (ARROW-PCF geometry shown in Fig 1). Such fibers have discrete transmission bands which exhibit strong dispersion arising from the scattering resonances of the high index cylinders.

Fig. 5 Schematic of ARROW-PCF geometry. Inclusions have a higher index than the background.

Fig. 7 Spectral evolution of the pulses as they propagate inside the ARROW-PCF. The average input power is fixed at 30 mW. Simulation results on left obtained from NLSE. Experimental results on righ retrieved from Frequency Resolved Optical Gating (FROG)